干旱区生态环境知识资源中心

Variable semi-arid climate characterized by precipitation patterns unfavorably distributed in space and time and high evaporation rates, reaching up to 100% of the incoming monthly precipitation, is a challenge facing water resources management in arid and semi-arid lands (ASALs). Kitui district in Kenya is an example of an ASAL environment, where water resources management issues are particularly important and sensitive. Sources of water are nearer to the people in the wet season, but as the seasonal rivers dry up, distance to water points get as far away as 25-30 km. Analysis of precipitation patterns, both in space and time, would be useful in understanding drought characteristics in order to develop strategies to capture, store and redistribute the available water. The spatial characteristics were determined through principal component analysis (PCA). Season lengths, drought severity and frequency were determined. The results indicated that, on average, the onset for the long rains (March-May) was centred on day 82 while cessation was on day 126. The longest season was 107 days during the long rains while the shortest lasted 7 days during the short rains (October-November). Severe droughts in the district were experienced in 1980, 1985, 1990 and 1995 using daily rainfall data for Kitui Secondary school (1975-1998) and Kitui Water Office (1981-1997). The largest seasonal total for the long rains was 768mm with a return period of 26 years while the smallest total was 81.1mm. For the short rains, the largest total was 1022.0mm with a return period of 16 years and the smallest total was 205.4mm. From principal component analysis, three eigen vectors were retained based on the Scree method. Kitui Secondary School had the highest communality, and was thus picked as the most representative station for further analysis. The spatial map was obtained by mapping the factor loadings at the station locations. Three homogeneous regions were delineated from these results indicating complex rainfall variability within the study area.